Updated 12:12 a.m. | If you had to pick a single event that brought Senate Majority Leader Harry Reid to the brink of using the "nuclear option" for executive branch nominees, look no further than Valentine's Day.

The Nevada Democrat's plan to pressure Republicans on their various filibuster attempts has its roots in the nomination of former Nebraska GOP Sen. Chuck Hagel to be Defense secretary. After that floor fight, senior Democrats began telegraphing, as early as March, their intentions to force a floor showdown.

Hagel's nomination dropped just weeks after Reid and Minority Leader Mitch McConnell, R-Ky., agreed to forgo radical changes to filibuster rules in exchange for GOP assurances that blockades of nominees would be kept to a minimum. But almost as soon as Hagel was named, Republicans sought to delay a vote on their former colleague.

“If this is not a filibuster, I'd like to see what a filibuster is," Reid said during consideration of Hagel.

Republicans were using the Hagel nomination as leverage to get answers from the Obama administration to a host of questions. That's pretty standard practice, but the stall made Democrats rethink their earlier decision to sidestep the more extreme filibuster rules changes that many in the caucus had been pressing for.

Reid filed a cloture motion and set up a vote on Hagel's nomination before the Presidents Day recess, to the anger of Republicans who said they had unanswered questions. Hagel fell just short of the 60-vote threshold.

“We do have an obligation of advise and consent — a constitutional responsibility — and we’re trying to carry this out," Sen. John McCain, R-Ariz., said during the Hagel debate. Hagel is now running the Pentagon, after winning confirmation shortly after the February break, but the episode stuck with Reid and other Democrats.

“All within the sound of my voice, including my Democratic senators and the Republican senators who I serve with, should understand that we as a body have the power on any given day to change the rules with a simple majority, and I will do that if necessary,” Reid said.

At the time, both Reid and Schumer appeared to be more concerned about judicial nominations, given that their comments came after Republicans successfully blocked Caitlin J. Halligan's nomination to the D.C. Circuit Court of Appeals.

But reading the tea leaves from Reid's April radio interview, it was clear he had begun to find a new voice on the filibuster issue, at least as it pertained to nominations. The changes are wildly popular within his caucus, but Reid had repeatedly pulled back in the past. Even with the latest proposal on administration nominees, Reid latched onto the least explosive change to the rules.

And he argued Monday that doing away with filibusters of executive branch nominees amounts to a minor tweak in the Senate's operating procedures, not a precursor to wholesale changes.

"My efforts are directed to save the Senate from becoming obsolete, to remain relevant and effective as an institution, and to do that, the Senate must evolve to meet the challenges of modern-day America. This is really a moment in history where circumstances dictate the need for change," the Nevada Democrat said Monday morning, speaking to a large audience at an event hosted by the Center for American Progress Action Fund. "Minor change, no big deal."

Republican Jeff Flake of Arizona saw that quote and responded just hours later on the Senate floor.

"It is a big deal. It has the potential to change this institution in ways that are both hazardous and unforeseen," Flake said. "The majority leader noted today that Senate rules have been changed 18 times in the past 36 years by a simple majority vote. There needs to be a qualifier here, a very big qualifier. This rule change will allow for the first time in Senate history majority-imposed cloture. That is not minor. That is a big deal."

Work continued Monday afternoon to try to find a way out of the procedural dispute before a series of votes set for Tuesday. Those nomination votes are intended to test whether Republicans will truly filibuster recess-appointed nominees to the Consumer Financial Protection Bureau and the National Labor Relations Board.

Cordray's nomination is slated to come up first on Tuesday, and sources said Cordray’s chances of drawing the 60 votes needed to beat back a filibuster had improved. But the NLRB nominees remained sticking points after the meeting, and Reid showed no signs of letting up the pressure on Republicans when he spoke to reporters late Monday evening.

Appearing briefly before cameras, Reid said, “We had a very good conversation. The conversation is going to continue tonight. Votes are scheduled for 10 in the morning.” (Later, Senate aides said votes would most likely come around 11 a.m., after the 10 a.m. swearing-in of Sen.-elect Ed Markey, D-Mass.)

But the chances of a compromise seemed slim. Earlier in the day, Reid was in no mood for a "gang" of senators working out a compromise that fell short of seeing seven executive nominees sail to confirmation.

"There have been gangs forming on this issue for a while," Reid said Monday. "My caucus supports where we are. I'm not concerned about gangs. That's gotten a little passe, frankly."

The "no big deal" posture is the opposite of the position taken by Republican critics in recent weeks, including Sen. Lamar Alexander of Tennessee, who has said the move could send the Senate down an inevitable path of becoming a majoritarian body like the House. In a clear shot at Reid, Alexander put building the nuclear repository at Yucca Mountain, Nev., near the top of his list of priorities for a GOP-led Senate.

On Monday, Reid called the Republican suggestions a bluff.

"If they get in, if they want to change rule by a simple majority, more power to them. I think ... they would rue the day they did it. They don't — they're not gonna do that," Reid surmised. "We're not gonna do that. It's all, you know, the sky is falling."